The long-term objective of this research project is to analyze the cellular and synaptic mechanisms of an example of associative learning and memory produced by Pavlovian conditioning. The studies proposed in this grant renewal will provide insights into general principles underlying memory for an associative experience following one-trial and multi-trial conditioning, and contribute to the elucidation of the events that are essential for the transformation of memory into a more enduring form, long- term memory. To address these goals, a multi-disciplinary approach to the study of associative learning and memory will be carried out in the marine mollusc Hermissenda, a preparation that has proven useful in biophysical, and biochemical studies of learning. The research will use a combination of cellular neurophysiological, biophysical, biochemical and behavioral techniques to study short- and long-term memory in intact and isolated nervous systems. One primary goal of the research is to identify proteins whose synthesis and/or phosphorylation are regulated by one-trial and multi-trial Pavlovian conditioning. We will compliment our studies of proteins regulated by conditioning by examining the contributions of signal transduction pathways to different stages of memory following one-trial and multi-trial conditioning. We have recently identified a beta-thymosin-like protein (CSP24) that is associated with an intermediate stage of memory consolidation. Studies are proposed to determine the specific role of CPS24 in time-dependent processes of memory consolidation produced by one- trial and multi-trial conditioning. The CS pathway of Hermissenda supports two examples of plasticity in identified cells of conditioned animals; synaptic facilitation or enhancement and enhanced excitability. We will determine if similar or different underlying biochemical mechanisms support the two examples of plasticity in identified cells of the CS pathway and examine the relationship between the cellular and synaptic mechanisms and the behavior of individual conditioned animals. An additional goal of this project is to determine and compare basic mechanisms of extinction of Pavlovian conditioning with time-dependent changes in retention of conditioning (foretting). Collectively, these studies of learning and memory will help to elucidate basic mechanisms of short- and long-term memory and provide insights into the relationship between memory mechanisms and clinical disorders of memory.